Chemical composition of O-(carboxymethyl)-chitins in relation to
lysozyme degradation rates
Carbohydr. Polym., 34 (3):
131 -- 139 (December 1997)Abstract
O-Carboxymethyl chitin (CM-chitin) is a water-soluble derivative of
chitin, be carboxymethylated in 3- and 6-positions to varying extents.
CM-chitins with a total fraction of O-substitution from 0.65 to 1.5
were prepared, and characterised by high-field proton n.m.r. spectroscopy,
allowing the determination of the fraction of O-substitution in positions
3 and 6, together with the fraction of N-acetylated units (F-A) The
carboxymethylation in position 6 was found to be larger than in position
3 in all fractions, confirming that the reactivity at OH-6 is larger
than at OH-3 in the carboxymethylation process. F-A of the CM-chitins
varied from 0.85 to 0.95, showing no systematic variation with the
total degree of carboxymethylation. These well-characterised CM-chitins
were degraded with hen egg white lysozyme. Initial degradation rates,
r: were determined from plots of the viscosity decrease (Delta 1/eta)
against time of degradation at pH 5.3 and ionic strength 0.1 (M).
It was found that the CM-chitin-lysozyme system obeyed a Michaelis-Menten
type of kinetics. The time course of degradation of CM-chitin with
lysozyme was non-linear, suggesting different degradation rates of
different sequences in CM-chitin. All r-values of CM-chitins were
higher than the highest rate determined for a partially N-acetylated
chitosan with F-A Of 0.6. The r-values were found to increase with
increasing F-A Of the CM-chitins, while r-values decreased with increasing
fraction of carboxymethylation. Furthermore, the results suggest
that carboxymethylation in position 3 has a larger effect on reducing
the rate than carboxymethylation in position 6. (C) 1997 Published
by Elsevier Science Ltd.